Radiation resistant closures are known in which inflatable tubes are utilized to move flexible conductive contact strips mounted on one member into conductive contact with a plate mounted on another member. An advantage of such a construction is that wear and tear of the contact strips is reduced because the strips are not subjected to the sliding action of the plate passing over the strips during opening and closing movement of the members relative to one another since the tube is inflated only after the members are in a closed position with respect to each other. For example, in U.S. Pat. No. 2,757,225, there is disclosed a door for a radio shielded enclosure having an inflatable tube contained in the edges of a door for a moving contact member made of a thin flexible sheet metal strip into contact with a conductive strip mounted on the edges of a door frame. Because the sheet metal strip is of solid construction, it is important that the door fit accurately in its frame so as to assure that all portions of the strip along its length will be in conductive contact with portions of the door frame when the tube is inflated. The need for accurate and close fitting between the door frame and door necessarily increases cost of production.
Conductive strips in the form of comb-like bowed fingers such as disclosed in U.S. Pat. No. 3,589,070 have been proposed where the bowed portions of the fingers flex outwardly of a member to which they are mounted to conductively engage a conductive plate mounted on another member. The individual fingers are easily flexed so that they will accommodate variations in spacing between the members. However since the strips containing the fingers are made of a light flexible material, such as beryllium copper, the fingers can be easily broken or bent out of shape, which if this occurs, can lead to impairment of radiation seal integrity.
It is therefore an object of my invention to provide for a closure for forming a radiation resistant joint which may utilize the advantages of conductive strips having a plurality of comb-like conductive bowed fingers and which at the same time will insure integrity of a seal even in the event one of the fingers is broken off or bent out of shape.
Broadly a radiation resistant joint according to the invention comprises first and second resilient electrically conductive contact fingers where each finger has a bowed portion comprising a part of a finger strip affixed to an edge of either a movable member or a fixed member. The second resilient fingers are affixed at one end in an overlapping relation to an end of the first fingers with both fingers being connected to an edge of one of the members. The free ends of the second fingers overlap and engages the bowed portions of the first fingers. Bowed portions of both fingers are adapted to engage a conductive plate on the other member with which the fingers are not connected so that the fingers form a conductive seal between the edges of the members.
Preferably the fingers are in a comb-like strip and are made of an electrically conductive material, such as for example, beryllium copper.
Further an inflatable tube is preferably positioned between the first fingers and the member to which it is connected such that when the tube is inflated, it will move the bowed portions of the first fingers and the free ends and bowed portions of the second fingers outwardly towards a conductive plate of the other member. When the tube is in a deflated condition, the natural flexure of the fingers will move the bowed portions of the fingers out of contact with the conductive plate. By this construction the fingers are protected from damage when the members are moved to a closed position with respect to one another where the conductive plate is free to slide over the fingers without contact during opening and closing movement of the members. Further use of an inflatable tube to move the fingers outwardly into conductive engagement with the plate allows the fingers to be positioned in a groove contained in the member the sides of which give further protection against inadvertent damage to the fingers.
The fingers and inflatable tube may be mounted on either the edges of the movable door member or on the edges of a fixed frame member surrounding the door. The conductive plate would be mounted on a corresponding edge of the other member. Preferably the fingers and tube extend around the complete periphery of either the door or fixed frame.